Antiaircraft fire control system



5 I 25, 1941. w CHAFEE 2,235,826

' ANTIAIRCRAFT FIRE CONTROL SYSTEfi Filed Feb. 21, 1938 4 Sheets-,Shget 1 March 25, 1941. E. w. CHAFEE 2,235,826

ANTIAIRCBAFT FIRE CONTROL SYSTEM Filed Feb. 21, 1936 4 Sheets-Sheet 2 HIS ATTORNEY I March 25, 1941. E. w. CHAFEE 'ANTIAIRCRAFT FIRE CONTROL SYSTEM Filed Feb. 21,1956 4 Sheets-Sheet a VaT March 25, 1941. E. w. CHAFEE 2,235,826

ANTIAIRCRAFT FIRE common SYSTEM Filed Feb. 21, 1936 4 Shegts-Sheet 4 H16 ATTORNEY V Patented Mar. 25, l

FIRE CONTROL SYSTEM Application February 21, 1936, Serial No. 65,125

In Great Britain January 23, 1936 15 Claims.

This invention relates to a means for directing antiaircraft gun fire. More particularly, it constitutes an improvement and further development of the antiaircraft fire control system disclosed in my prior United States patent application now Patent #2,065,303, dated December 22, 1936, for Fire control system, joint with Hugh Mur'tagh and S. G. Myers, which is generally referred to as the plan projection system of'fixed rectilinear coordinate axes. The system described in said patent is particularly adapted for land batteries, and the purpose of the present invention is to modify and adapt such system to a naval antiaircraft system while retaining the advantages of simplicity and accuracy characteristic of this system.

A. further object of the invention is to improve the aforesaid system so that it is adapted for gliding targets as well as targets flying substantially horizontally.

According to my present invention, I propose to retain the system of rectilinear coordinates along axes fixed in azimuth with reference-to a datum line such as a north-south line, for the resolution of the present ground course of the target into components from which the rate of movement along each coordinate axis is obtained. In order to use this system on shipboard, I propose to feed into the director true or absolute azimuth (or compass) angles and true or absolute elevation angles with respect to the horizontal instead of relative train angles and relative elevation angles with respect to the 'shlps fore and aft line and plane of the ship's deck, respectively. In order to do this, I provide a correction device which resembles a trunnion tilt c'orrector V Wittkuhns, said device being controlled in both azimuth and elevation by the gyro-compass and gyro or other vertical used, and operating to stabilize in both azimuth and elevation the line of sight of the range finder or Other sighting device. I supply continuously to the computer the true present elevation angle (E0), the true present sight angle (A0), and the present slant range (Du) From E0 and Do, I obtain the present horizontal range (Ru) and the altitude (Ho) by means of a computing mechanism which first converts the angle E0 into the cotangent function of the angle. Two'three-dimensional cams are translated according to said cotangent E0 and are rotated from a shaft, whose motion eventually becomes proportional to Ho, to solve for the two unknowns, horizontal range (R0) and altitude (I-Io) by matching a dial turned from the lift of 'one cam pin with a dial turned in accordance proportional to altitude (Ho). The lift of the 5 pin on the second cam gives R0, which is fed into the machine substantially as the horizontal range is fed in in the aforesaid prior Patent 2,065,303, and resolved into components along rectangular axes, and the rate of change of each component measured, from which the future position is obtained by multiplying said rates by the time of flight of the shell and adding the component changes of position thus obtained to the coordinates of the present position.

In case the altitude is changing, the dial actuated from the lift pin on the first mentioned cam will not stay matched with the slant range dial Do as elevation angle alone is fed in, and therefore the operator must also feed in the changed altitude. Preferably a variable speed drive is arranged to set in the continuously changing altitude to keep the Do dials matched. In such case, the rate of change of altitude is derived, which is also multiplied by the time of flight of the shell to determine the change in altitude as well as the change in azimuth during that period.

The above combination of the two three-dimensional cams indicates when a target is not flying horizontally and also provides a means for separating that part of the change in E0 due to change in altitude from the change in E0 due to change in position-in the horizontal plane.

According to my invention, operation of the system remains unaffected by the course, roll and pitch and yaw of the ship, since the lines of sight of the observing telescopes are stabilized. A correction for ship's speed is introduced in the same manner as the wind correction in the aforesaid prior patent, namely, it is treated as a wind blowing with equal and opposite velocity to the ship's speed and is set in as an additional wind correcrespect to the fore and aft line of the ship and the plane of the ship's deck. To effect this re conversion, I employ a second trunnion tilt corrector device such as shown in the aforesaid Patent 2,069,417, into which is fed the future abso-- lute angles from the computer and the compass bearings and the true vertical from the gyro-compass and the gyro-vertical, respectively. Said second corrector therefore sends to the gun quadrant elevation from the ship's deck and train angle with respect to the ship's fore and aft line, the gun being set therefrom either by the follow-thepointer system or automatically. By this method of obtainingthe absolute or true elevation for the line of sight and for the gun elevation from the same gyro-vertical, any minor error from the true vertical in said gyro has no effect on the true positioning of the gun.

In the drawings,

Figs. 1--A and 1-13 are a diagrammatic representation of a computer constructed according to my invention, part of the same being shown in l--A and the second part in 1-3.

Fig. 2 is a diagram representing the position of the computer in the complete naval fire control system.

Fig. 3 is a diagram representing the trigonometry of the problem involved, in three dimensions.

Fig. 4 is a diagrammatic development of one of the resolving mechanisms employed in the computer.

Fig. 5 is a diagram explanatory of certain features of the computing mechanism.

According to my system, the line of sight from the range finder R is stabilized both in azimuth and elevation from a gyro compass and gyro vertical through a trunnion tilt corrector or eliminator, the general scheme being shown diagrammaticaliy in Fig. 2. In this figure, the ship's gyro compass is represented at C, the ,gyro vertical at V, the range finder at R and the trunnion tilt error eliminator at M. As described more completely in the aforesaid Patent 2,069,417, the roll and pitch and yawing of the ship are taken out of the line of sight of the range finder through the trunnion tilt err'br preventer M.

The device M is positioned in azimuth and elevation by the range finder through transmitters TA and Tr on the range finder actuating repeater motors RA and RE at the correctorr At the same time the compass C prevents turning of the ship from affecting the same through the compass repeater motor Ca and the device is in effect stabilized from the gyro vertical V through the transmitters Vi'I and VaT thereon, actuating repeater motors vlR and Van. The regenerated or true azimuth and elevation angles are thentransmitted from transmitters T'a and TE, respective- .through repeater motors R'a and R's. Transmitters TA and Ta also transmit the true azimuth bearing angle Au and true elevation angle E0 to the computer through the lines marked I and 2, and the slant range is transmitted from transmitter Ta through line 3.

Referring now to Fig. 1-A, the. true elevation angle E0 is represented as coming in on dotted line I and the true azimuth angle on dotted line 2, while the slant range comes in on'dotted line 3, which lines represent the electric wires leading from the several transmitters Tn, Ta and Ta on the range finder to the elevation repeater motor 4, the azimuth repeater motor 5 and the range repeater motor 8, respectively. Motor 4 operates coarse and fine elevation angle indicators E0 and E0, one being geared to rotate at a multiple of the speed of the other. Each indicator is provided with a follow-the-pointer index I, l, the indexes being connected to be turned from a gear sector 8 on an arm 9 pivoted at It). This forms part of a mechanism for solving for the unknown altitude Ho and the unknown horizontal range R0 from the known elevation angle E0 and the known whole or slant range Do.

- From an inspection of Fig. 3 it will be apparent that the following equations may be written:

(1) Ro=Ho cot E0 (2) Ho=Do sin Eowhich may also be written Do=Hn cosec E0 The mechanism solves for the unknowns in accordance with these equations.

The arm 9 is provided with a slot l l with which a pin on a nut I2 engages, the nut being threaded on rotatable threaded shaft I3. Said shaft is rotated from the E0 handwheel l4 until the indexes on the E0 dials match the pointers. Since the distance from pivot ID to the threaded shaft I3 is fixed, it follows that as E0 changes, the distance of nut l2 from the right hand end of threaded shaft 53 (or more precisely, from the point at whichthe perpendicular through pivot in intersects said shaft) changes proportionally to cot Eu. If, as shown diagrammatically in Fig. 5, the scale of the mechanical representation of the present elevation triangle formed by arm 9 and shaft I 3, with E0 as the included angle therebetween, is arbitrarily made such that the fixed vertical leg (i. e., the distance of pivot ID from shaft I3) represents the maximum target altitude for which the system is designed, (and which will be assumed, by way of illustration, to be 8,000 yards) then the base of the triangle, which is the distanceofnut i2 from the right-hand end of shaft I3, is equal to the'product of this maximum altitude and the cotangent of E0 and therefore has a valueequal to 8,000 cot E0 or VH0 XR In other words, the base of the triangle represents R0 on a scale which varies with altitude and is equal to R0 when the altitude is a maximum, here taken as 8,000 yards. At the same time that it shifts nut l2 the rotation of handwheel l4 shifts laterally the three-dimensional cams l5 and IS, the shaft ll of said handwheel being geared to the threaded shaft I! on which a bracket l8 supporting the cams is mounted. Therefore these cams will be translated proportionally to cot E0 and since shaft i1 is connected by gearing with shaft 53, the position of bracket l8, measured from a reference position, also represents cot E0 on a suitable scale, and in the present case has a value of 8,000 cot Eo. such that as it is rotated and translated by means to be described, the lift of the cam pin [9 thereon is proportional to the slant range Du corresponding' to the value of E0 according to which the cam is translated and the value of Ho according to which it is rotated (see Equation 2). The

cam pin lli'therefore is connected to rotate the The contour of cam I5 is matched. It is obvious that a power driven follow-up may be employed if desired. When the pointers are matched, the angular position or rotation of the cam I5 represents Ho. Therefore the cam I6 will likewise be positioned rotationally in proportion to Ho and it is translated proportionally to cot Eo. This cam likewise is provided with a cam pin M. This cam is so laid out that when the translation is proportional to cot E0 and the rotation proportional to Ho, then the lift of the cam pin 2| will be proportional to horizontal range R0 (Equation 1). Said pin is therefore shown as positioning a dial Re which has a followthe-pointer index 23 on a concentric outer dial. The two cams are shown as rotated from a gear 24 and a long pinion 25 which, inturn, is set from either one or the other of the Ho handwheels 26 or 21. The index 23 is turned from the horizontal range or R0 handwheel 28 which turns the index through shaft 28', differential 29, shaft 30, shaft 3| and worm 32. When index 23 is matched with the pointer on the inner R0 dial by turning handwheel 28, R0 is set into the computer through the shafts 30 and 33.

With the foregoing arrangement it will be evident that means are provided to indicate when a target is not flying horizontally. In prior arrangements it has been recognized that changes in E0 may be due not only 'to change in position in the horizontal plane but to change in altitude, but the practice has been to assume the craft to be flying at a constant level. With the above arrangement, however, the observer is enabled to separate that part of the change in E0 due to change in altitude from the change in E0 due to change in position in the horizontal plane, because in case the altitude is changing, the index 20 will not stay matched with the slant range dial D0 when only the elevation angle of the target (E0) is fed in and therefore changed altitude must'also be. fed into the machine through the handwheel 26 or 21. The latter is used primarily for setting up an original altitude or when the rate of change of altitude is not constant. In case the target is diving or climbing steadily, the handwheel 26 is used to set up a rate of change of altitude. .This handwheel, it should be noted, positions the change speed member, 1. e., ball 35, of a variable and reversible speed gear of which the disc 36 is constantly driven as from a motor 31. The ball drives a cylinder 38 which is connected through a differential 39 to the shaft 21' of handwheel 21 and to shaft 40 which rotates the pinion 25, the altitude being shown on Ho dial 40. At the same time the changing altitude H0 is set into the machine through shafts SI, 62 and 43.

When the condition of constant altitude Ho obtains, it is not necessary to position index 23 continuously by turning handwheel 28 since once this index and the pointer on the inner R0 dial are matched, they will remain matched due to the rotation of index 23 by means now to be described. The rotation of shaft I1, measured from a reference position, as noted above, has a value of 8,000 cot E0 due to the fact that 8,000 yards is the value of the vertical leg of the triangle in the cotangent solving mechanism mechanically representing the present elevation triangle as shown in Fig. 5. If, therefore, a target at 8,000 yards altitude is being tracked, the rotation of shaft I1 represents R0 directly.

It is seen in Fig. 1-A that the value 8,000 cot E0 is set into the computer by way of diflcerential 13 geared to shaft I1, differential 29, shaft 30 and shaft 33. By means of a nut moving along a threaded portion of shaft 42, a ball 1| bearing tion of which is controlled both by the altitude displacement and altitude rate settings of handwheels 21 and 26 respectively. Ball H is at the center of disc 10 when the value of H0 is 8,000 yards. Therefore, at 8,000 yards altitude, roller 12 does not rotate and introduces no motion into differential 13 and consequently, assuming that no motion is introduced into differential 29 by way of shaft 28', the rotation of shaft 33 reproduces the rotation of shaft I1 and represents 8,000 cot Ea. If, however, the altitude Ho has some value which is less than the maximum, ball 1| will be positioned away from the center of disc 10 a distance representing the difference between 8,000 yards and this value, and since the rotation of disc-10 is proportional to cot E0, the rotation of roller 12 will be proportional to (8,000Ho) cot E0 and by a suitable choice of constants can be made to represent this value. The output of differential 13 (with proper directions of rotation) and the rotation of shaft 33 then become: 8,000 cot Eo (8,000-Ho) cot E0 =Ho cot Eo It is seen that the multiplying device comprising disc 10, ball 1! and roller 12 in combination with differential 13 provides R0 computing means operating in parallel with cam I6 and that the results of these two computations are shown on the outer and inner R0 dials respectively.

Shaft 3|, driven from shaft 30, drives through worm 32 the outer Ro dial bearing index 23, said dial having teeth out in its periphery, and as the rotation of shaft 3| represents range as computed by the variable speed multiplier, the R0 pointer on the inner dial and index 23 should remain matched once they have been brought into coincidence, as for instance by rotating handwheel 28, if altitude remains constant. The distinction between the change of elevation angle due to changing range and that due to changing altitude will now be apparent since it is seen that range handwheel 26 has to be operated only if a change of elevation angle occurs due to change of altitudebut not if a change of elevation angle occurs due solely to change of range.

While the cotangent solution is satisfactory for sizable angles of elevation, when the angle becomes small I prefer to use the angle itself instead of the cotangent function. To this end, the bar 9 towards its lower end is curved so that the travel of the nut I2 along the shaft I3 at low angles will be approximately proportional to E0. In this case the handwheel 28 is rotated until a counter 46 reads the same as the slant range dial Do, thus taking the value of slant range Do 'and using it as horizontal range Re, which is sufficiently accurate for small angles. This value of R0 is fed into the machine through shafts 30, 33, as before. It is also communicated to shaft to position .a threaded carriage 46 proportionally to R0. A pivoted arm 41 is rotated automatically from a cam surface 68 on the carriage I8 so that the angle between the arm 41 and the horizontal is a function of the angle E0, preferably a multiple of the small angles involved. The altitude handwheels 26 and 21 are set to position the in contact with arm 41 as determined by'indicating means not shown, the shaft 48 rotating the threaded shaft 50 on which the hub of the arm is threaded. This sets up a mechanical triangle whose base represents R0 (taken as equal to Do), whose altitude represents Ho and whose acute base angle is proportional to E0. H0 is theshown as actuating coarse and fine dials An and Ad, each having a follow-the-pointer index 5| and 5|. These indices are maintained matched with the dials, preferably by handwheel 52 which rotates the shafts 55 and 58 to set the changing A0 into the machine.

As explained in the aforesaid prior Patent 2,065,303, I prefer to project the movements of the target into the plane of the, ground and to resolve its ground course into a: and y components, say NS and EW, and to obtain the rate of change along each component. To this end, I provide resolving mechanisms shown diagrammatically in Fig. 1B at 51 and 58. These mechanisms (see Fig. 4) comprise essentially a flat disc 59 having a spiral groove in its upper surface in which engages a pin 58. engages a slide 5| mounted in a slot 62 in a second disc 53. It also engages a slot 68 in a bracket mounted for rectilinear movement only in a NS direction, for example. The disc 63 is shown as rotated in accordance with the angle A0 from shaft 56 through shaft 51' and suitable gearing (not shown), so that the slot 82 is positioned in azimuth in accordance with the angle A0 that the line of sight makes with the N-S line. The disc 59, on the other. hand, is rotated in accordance with the horizontal range R.) from shaft 83 and shaft 58' through a differential I58 also connected to shaft 51' to prevent the range being changed by changes in A0. Therefore the slide 8| will be given a radial position in the slot'proportional to R0 and its direction of displacement will be in accordance with the angle A0. The as component of this movement, say the NS component, will be imparted to the bar 65. The 1 or EW component is imparted to a corresponding bar 65' mounted on an identical resolving mechanism 58 in which the slot 52' is maintained at right anponent, which may be done as in the prior patent by means of tachometers 86 and 65'. Periodically the movement along each component is timed by its tachometer and the rates set in by rotating the respective :r and 1 handwheels 81 and 61' to match the indices 68, 58 thereon with the tachometer pointers.

Said rates are then multiplied by the time or flight of the shell by any suitable means, such as cams 59 and 69'. Said cams are arranged to be moved axially in accordance with the time of flight of the shell obtained from the movement of a cam pin 18' on cam T. The cams 69 and 69 are respectively rotated from the handwheel 81 through cross shaft-1l' and long pinion H2 and from handwheel 61' through gearing 13' and pinion 12'. The lifts of the pins 14 and 15 on the two cams 69 and 69' are proportional to the dis- Said pin also Cam. T is shown as moved axially from future altitude, the shaft 18 thereof being rotated from a gear 11 driven by an elongated pinion 18. Said 1 pinion, in turn, .is rotated from Ho shaft 48 through a differential 19, the change in height during time of the flight of the shell being added from shaft 88 to give the predicted height (Hp),

longitudinally from the Ru shaft 88 through a differential 8| into which is also-fed the change in range from the range difference motor 82 to give predicted range (Rp). As shown, the differential 8| rotates shafts 83 and 84, the latter rotating the screw 85 to position travelim carriage 86 threaded thereon, which moves the cam axially. For convenience, the fuse setting cam F and the quadrant elevation cam QE are mounted on the same shaft 18 as cam T so as to be rotated and positioned axially therefrom. The 'lift of cam pin 18' on cam T is shown as shifting axially the cams 59 and 89 through a cross bar 81.

A tachometer 88 similar to the tachometers 58 and 68' may be used for determining the future altitude. Present altitude, when changing, continuously rotates the shaft 48, thereby rotating a disc 89 forming a part of a variable speed mechanism. The ball or roller 98 thereon is positioned from the time of flight pin 18 by being connected to move radially with the axial movement of the cams 59, 69'. Therefore this mechanism acts to multiply the rate of change of altitude by the time of flight of the shell, which ro tates cylinder 9| at a rate proportional to the change of altitude. The cylinder 9| rotates the tachometer 88 at that rate, which therefore measures this rate and gives the change of altitude, which is set in by rotating the handwheel 92 to match the index 93 with the pointer. The value so set in rotates the shaft 88 and differential 19 to add the change in altitude that takes place during the time of flight of the shell to the present altitude, thus rotating shaft 8| and pinion 18 according to the future or predicted altitude Hp.

The cam pins 14 and 15 control mechanisms 94 and 95, which may be similar in construction to the mechanisms 51 and 58, but which actconversely thereto to convert the future coordinate positions of the target into future range and bearings. For this purpose it is desirable to provide follow-up or power driven systems for actuating the mechanisms, as described more completely in my aforesaid Patent 2,065,303. The cam pins are shown as positioning pairs of reversing contacts 95 and -98', respectively, the trolleys or brushes of which, 91 and 91, are mounted to move with' the slide bars 98 and 98', respectively. Thebar 98 is positioned primarily from the corresponding bar 55 of the mechanism 51 through shaft 99, but has an additional movement imparted thereto through differential I88 to introduce the change in the a: position thathas taken place during the time of flight. Similarly, the bar 98' is positioned from the bar 55' through a differential Hill to introduce the corresponding changes in the 1/ position. Therefore the angular position of the discs 59 of reas hereinafter explained. The cam is moved I solvers 94 and 95 will represent the future range Rp and is shown as taken off through shafts IM and IN to rotate the shaft 83, while the angular position of the disc 63, containing the radial slot, shows the future angle Ap and is transmitted through shafts I02 and I02 to shaft I03. In practice, the shafts 83 and I03 are rotated from the range difference motor 82 to turn the discs 59 and -63 thereof and the azimuth difference motor I04, respectively, said motors in turn being driven from the contacts 96 and 9B the motors being connected to said shafts through differentials' BI and I05, respectively. Box S represents a quadrant switch more completely described in the aforesaid Patent 2,065,303. The future azimuth angle Ap is transmitted, with whatever corrections needed, through a transmitter I06 to a second trunnion tilt eliminating device M through wires I30.

The quadrant elevation cam QE, it will be remembered, is positioned axially in accordance mitted to the trunnion tilt corrector through Similarly, the

transmitter H and wires I3I. fuse setting is derived from the cam F on shaft 16 from a lift pin III, into which corrections may be introduced through handwheel N2, the fuse setting being transmitted from transmitter H3 and wires I32.

As in my prior patent, the wind correction is preferably introduced as a component rate correction along the my components, this being introduced into the settings of tachometers 68 and 68'. Preferably, also, I employ a similar means for correcting for the speed and course of the firing ship. As far as the effect of the wind is concerned, the motion of the firing ship may be treated as an apparent wind in the opposite direction to the movement of the ship, and therefore this apparent wind may be resolved into my components and corrections introduced in the same manner as the true wind. For the above purposes, I have shown two resolving mechanisms. At H6 is the resolving mechanism for the true wind. This may comprise an inner dial II 6' set in azimuth by a handwheel IE until the slide bar IIG thereon lies in the true direction of the wind, as indicated by the reading of index I5I on scale I52. Said scale is prefer- "ably made adjustable in case the my components are not truly NS and EW. The bar is then adjusted by turning the pinion III until the length thereof to the right of the pinion represents the velocity of the wind. This velocity is then resolved into a: and y components by positioning the cross hairs H8 and H9 from handles II8 and II9 until they intersect at the zero index on the bar, thereby rotating the shafts I and lil.

A similar resolving mechanism I22 is provided for the ships course and speed. In this case, however, thedial I53 thereof is rotated from a repeater compass I23 so that it is maintained fixed in azimuth regardless of the tuming of the ship. Slide bar I20 is adjusted in accordance with the ships speed and the two components are then determined by means of the cross bars I25 and I26, as before, by turning" handles I54 and I55. The component values of the true wind and apparent wind are then added algebraically through differentials I21 and I21 and the result led to the two tachometers 68 and 68' through differentials I28 and I28, where the my rates are added. The indices are thus displaced, and the handwheels 01 and 61' must be rotated accordingly to keep them matched with the tachometer pointers. In my solution of the problem, the speed of the firing ship is otherwise neglected, being taken into account as the apparent speed and course of the target.

The final predicted quadrant elevation, and

bearings are transmitted from the computer through lines I30 and I3I, but are first led through a second trunnion errordevice M' to correct the same for trunnion tilt errors and to reconvert them into angles-with respect to the ship's deck and fore and aft line before reaching the gun G. The device M is operated identically with the device M, except that it is positioned in accordance with the trunnion position of the gun (i. e., future bearings) instead of the trunnion position of the range finder (present bearings), and into which are fed the future bearings and elevation insteadof the present bearings and elevation. The gun will therefore be positioned in the proper position to hit the target at all times regardless of the roll and pitch of the ship.

It will be understood that suitable indicators may be provided wherever desired throughout the instrument. For instance, I have shown a dial Ap on the future bearing transmitter E00,- a dial Ep upon the quadrant elevation transmitter, and a dial Fp on the fuse transmitter. I have also shown a dial I60 connected to the range difference motor 82, indicating the range changes, and a dial IGI connected to handle 20, indicating the rate of change of altitude.

Also, while I have referred to the a: and y axes as E--W and N- -S, it will be understood that they may be taken in any direction as long as they remain fixed in azimuth ,during a period of I fire. Preferably, the fore and aft line of the ship at the time of throwing the computer into use is taken as the y axis.

As many changes could be made in the above construction andmany apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted'as illustrative and not in a limiting sense.

Having described my invention, what I claim and desire to secure by Letters Patent is:

1. In an antiaircraft director for computing proper gun elevation, means to set in slant range (Do) and the elevation angle (E0) of the target, means to compute present altitude (Ho) and present horizontal range (R0) from said transmitted quantities of slant range and elevation angle, including means for mechanically generating a displacement proportional to the cotangent of the elevation angle as one side of a rectangular triangle having its hypothenuse proportional to slant range and said elevation angle (E0). included between said side and hypothenuse, and a pair of three-dimensional cams positioned in one dimension by said displacement and in the other dimension by an arbitrary quantity until the lift of the pin on one cam is proportional to slant range, whereby said arbitrary quantity becomes proportional to present altitude (Ho) and the hit of the pin on the other cam simultaneously becomes proportional to horizontal range (Re).

2. In an antiaircra'ft director for gliding targets, means for continuously setting slant range (D0) of the target into an indicator. means for continuously setting in elevation angle (E0) of the line of-sight, means to mechanically solve simultaneously for the unknown horizontal range (R0) and altitude (Ho), comprising a pair of coaxial three-dimensional cams each having a cam pin, one cam pin adapted to match said indicator, the other cam pin adapted to operate a range dial, means to position said cams in one dimension in accordance with the cotangenlt function oi said elevation angle, and arbitrary setting means to position said cams in the other dimension to such values of altitude (Ho) as to keep said slant range indicator matched, whereby said range dial is caused to indicate present horizontal range (R0) and the set value of altitude (Ho) represents actual target altitude.

3. In an antiaircraft computer to which functions of target position including slant range (Do) and elevation angle (E0) are continuously supplied, an elevation angle indicator, a slant range indicator, a computing mechanism computing horizontal range (R0) from said slant range (Do) and said elevation angle (E0), including means for arbitrarily feeding height (Ho) and horizontal range (R0) into said computing mechanism at such a rate as to simultaneously match both of said indicators, a measure of actual target height (Ho) and actual horizontal target range (R0) being obtained when said indicators are matched.

4. In an antiaircraft computer into which elevation angle (E0) and slant range (D0) are continuously supplied, an elevation angle indicator, a slant range indicator, a triangle mechanism of fixed height and variable base and an acute angle, in which said angle is kept at the elevation angle (E0) to give a base length representing the cotangent of said angle (cot E0), a second mechanism in which said cotangent of said angle is combined with slant range (Do) to give altitude (Ho), a third mechanism for combining the cotangent of said angle (cot E0) and altitude (Ho) to give horizontal range (Be) on a range indicator, a fourth mechanism to also calculate said same horizontal range and connected to match said range indicator, whereby with constant altitude said range indicator remains automatically matched regardless of change of horizontal range, said indicator becoming unmatched only upon change of altitude.

5. An antiaircraft director as claimed in claim 1, in which an alternative approximate solution is employed as the elevation angle (E0) drops below a given value, said solution being obtained by means of an assembly of members forming a triangle in which two sides are each proportional to slant range (Do) I and in which the included angle is the elevation angle (E0) 6. An antiaircraft fire control apparatus as claimed in claim 2, having a variable speed device in said arbitrary setting means (Ho), whereby said indicator is kept matched automatically when the proper rate of change of altitude has been set up.

7. In an antiaircraft director for computing the proper gun elevation from instantaneous values of angular elevation and slant range of a target continuously transmitted from a range finder, a computing mechanism including means finder data, means providing an alternative soiution in case of substantially horizontal fire as altitude approaches zero, one or more elements 5 being common to said two means and said alternative solution including initially equating slant range and horizontal range, means for continuously determining gun elevation from future target-positional data and means for-selectively supplying said data continuously to said last means from one of said first two means.

8. Means for computing proper gun elevation for antiaircraft guns from slant range (Do) and angular elevation (Es), continuously supplied by a range finder, comprising cam means for con tinuously solving the equations R0 (horizontal range) =Ho cot E0 (altitude times the cotangent of the elevation angle), second cam means for simultaneously and continuously solving the 2 equation Ho- (altitude) =Do sin E0 (slant range j times the sine of the elevation angle), and multiplier means for a second simultaneous and continuous solution of said first named equation, whereby altitude and range are continuously 2 obtained.

9. In antiaircraft fire control apparatus, means for continuously obtaining the altitude of a moving target from slant range (Do) and angular elevation (Eo) continuously supplied by a range 3 finder, comprising a first means for obtaining horizontal range (R0) therefrom, a second means for obtaining horizontal range therefrom, means to match the output of said first means with the output of said second means comprising means 3 to introduce arbitrary settings proportional to unknown altitude (Ho) until said outputs remain matched, whereby true altitude is simultaneously obtained;

' 10. An antiaircraft fire control apparatus as 4 claimed in claim 9, having a variable speed device in said second means for obtaining horizontal range, to compensate for altitude changes.

11. In an antiaircrai't fire control device as claimed in claim 2, a follow-up pointer for said 4 range dial, second means to solve for unknown horizontal range including a variable speed drive connected as a multiplying device to multiply said values of the cotangent of said elevation angle by the diilerence between an assumed fixed 5 maximum altitude and said computed altitude Ho, diflerential means to combine the product with a multiple of said cotangent value proportional to said flx'ed altitude, and means to connect said follow-up pointer to said differential 5 means, whereby said pointer automatically remains matched as long as said altitude Ho remains constant. I v 1 12. In an antiaircraft fire control apparatus, an indicator to receive elevation angle E0 of a 6 target, a follow-up pointer associated with said indicator, a cotangent solving mechanism for said elevation angle adapted to match said pointer to saidindicator, a pair of three-dimensional cams positioned in one dimension by said mech- 6 anism according to said cotangent value, a slant range receiver having a dial to indicate received slant range, a follow-up marker for said dial operated from a cam pin on one of said cams, a range dial operated from a cam pin on the other cam, a follow-up marker for said last named dial, a range solving mechanism to operate said last named marker, altitude setting means to position said cams in another dimension to match said first named marker to said first 7 named dial, and means to operatively connect said range solving mechanism to said cotangent solving mechanism'and to said altitude setting means, whereby both said markers remain auto-'- matically matched to their respective dials as long as the value of altitude once set in remains constant.

13. In an antiaircraft fire control apparatus, means for continuously obtaining the altitude of a moving target, comprising means for feeding into the apparatus from a range finder values representing slant range (Do) and angular elevation (E), means for obtaining a fictitious value representing horizontal range (R0) in terms of a permanently fixed value of altitude (H), a pair of three-dimensional cams each having a cam pin, means for positioning both said cams in one dimension from said first named value, means for positioning both said cams in another dimension by an arbitrary setting. proportional to unknown altitude (Ho), such that the lift of one cam pin is proportional to said known slant range and the lift of the other cam pin is proportional to true horizontal range (R0) a followthe-pointer mechanism associated with said last named cam pin, a correcting means controlled by said altitude (Ho) to correct said fictitious value of R0 for the altitude difference (HHo), and means to introduce said corrected value of R0 into the computer and into said follow-thepointer mechanism, whereby said mechanism remains matched automatically as long as altitude Ho remains constant.

14. In an antiaircraft fire control director, data converting means for deriving data including altitude (Ho) from observed data relating to the position of an aerial target, including slant range (Do) and elevation angle (E0) comprising an indicator for slant range, a calculating device controlled partly by a function of said elevation angle (E0), and means for additionally controlling said calculating device to position a part to match said indicator, said calculating device being constructed and arranged so that when said indicator is matched, the quantity set into said last named means for controlling said calculating device is thereby made proportional to the altitude (Ho) oi the target.

15. A system of antiaircraft fire control adapted to shipboard use, comprising a range finder for measuring present slant range of a target, a sight rotatable in azimuth and elevation relative to the ship, means for continuously measuring the angular elevation and azimuth of the line of sight relative to ship's axes, means for continuously measuring the positions of said ships axes relative to fixed axes, a first corrector for converting positional data relative to said ships axes to data relative to said fixed axes, a second corrector for converting positional data relative to said fixed axes to data relative to ship's axes, a computer for calculating future positions of said target in accordance with a plurality of factors including present slant range, angular elevation and azimuth and rates of change thereof, all relative to said fixed axes,

means for continuously transmitting the present angular elevation and azimuth of said target relative to said ships axes to said first corrector, means for continuously transmitting the converted data therefrom to said computer, ,means EARL W. CHAFEE. 

